Why are fossils of Mesosaurus separated by thousands of kilometers of ocean when the species once lived all together?

Students play the role of geologists working for the fictional Museum of West Namibia to investigate Mesosaurus fossils found both in southern Africa and in South America. They learn that the surface of the Earth has changed dramatically over the Earth’s history, with continents and ocean basins changing shape and arrangement due to the motion of tectonic plates. As the Earth’s surface changes, fossils that formed together may be split apart.